Device and method for dynamic processing in water purification

ABSTRACT

A transformational approach to water treatment is provided that incorporates membrane-free filtration with dynamic processing of the fluid to significantly reduce treatment times, chemical cost, land use, and operational overhead. This approach provides hybrid capabilities of filtration, together with chemical treatment, as the water is transported through various spiral stages.

CROSS REFERENCE TO RELATED PATENTS AND APPLICATIONS

This application is related to co-pending, commonly assigned U.S. patentapplication Ser. No. 11/606,460, filed Nov. 30, 2006, entitled “ParticleSeparation and Concentration System,” and commonly assigned, co-pendingU.S. patent application Ser. No. 11/936,729, filed on Nov. 7, 2007,entitled “Fluidic Device and Method for Separation of Neutrally BuoyantParticles,” and naming Lean et al. as inventors.

BACKGROUND

Conventional municipal water treatment (MWT) includes multi-stagefiltration and sequential process steps for coagulation, flocculation,and sedimentation. Typically, a minimum of two stages of filtration mustinclude coarse 2-3 mm mesh filters at the inlet and 20-40 μm multi-mediafilters for finishing although many utilities have more intermediatefiltration steps. The hydraulic retention time (fluid residence time) inthe combined coagulation-flocculation-sedimentation process can be 5-10hours long, depending on the quality of the source water.

With reference now to FIG. 1, a conventional water treatment facility isillustrated. This, of course, is merely an exemplary system. As shown, asystem 10 includes a source 12 of any of a variety of types of fluidsuch as surface water, ground water, waste water, brackish water,seawater . . . etc. This water is fed to a screen filter 14—which istypically operative to filter out particles in the 1 mm to 3 mm range.After these relatively large particles are removed, a pH adjustment ismade to the water and potassium permanganate (KMnO₄) is added to thesupply in a carbon reactor/mixer 16. This chemical is typically addedfor taste and odor control. Other substitutes may include ozone andother oxidizing agents. Next, chlorine is added to the supply and mixedin a mixer 18. Flash mixing wherein coagulants (e.g., Alum, FeCl₃, ACH,etc.) are added is then performed in a flash mixer 20. Flocculants—madeof long chain polymers with a high molecular weight—are added at aflocculation stage and mixed in a slow mixer 22. The supply is then sentto a sedimentation tank 22 where particles settle out of the effluent asa result of gravitational forces. The flow from the sedimentation tankis then provided to a multimedia filter 26 which operates to removeremaining small particles. The output of the system can then be used fora variety of purposes. In one form, chlorine is added to the output. Themultimedia filter is frequently backwashed, and the backwash isoptionally fed back to the water source. In this backwash, or feedback,path, a dewatering stage 28 may be provided whereby water is providedback to the source and sludge is removed.

As noted above, the water purification process described requires asubstantial amount of time. With reference now to FIG. 2, it is seenfrom an example flow 50 that the basic steps include rapid mix(including coagulation), flocculation, sedimentation, and filtration. Asshown, the rapid mix stage 52 takes 30 seconds to 2 minutes to complete.The flocculation stage 54 requires 20 to 45 minutes of processing time.Sedimentation 56, or any other alternative solid removal process,typically requires at least 1 to 4 hours (and possibly up to 10 hours)of processing. Last, filtration 58 also requires a definitive amount oftime. The extended time periods are not only a problem formunicipal-type purification systems but also water purification systemsthat are used in other environments, such as a lab environment.

Therefore, it would be desirable to have available an alternative watertreatment system that can more efficiently and effectively purify water.

INCORPORATION BY REFERENCE

This application is related to co-pending, commonly assigned U.S. patentapplication Ser. No. 11/606,460, filed Nov. 30, 2006, entitled “ParticleSeparation and Concentration System” and commonly assigned, co-pendingU.S. patent application Ser. No. 11/936,729, filed on Nov. 7, 2007,entitled “Fluidic Device and Method for Separation of Neutrally BuoyantParticles,” and naming Lean et al. as inventors which are bothincorporated herein in their entirety by this reference.

BRIEF DESCRIPTION

In one aspect of the presently described embodiments, the systemcomprises an inlet to receive water from a source, a filter stageoperative to filter first particles, a mixing stage operative to receiveand coagulate the filtered water, a spiral stage operative to receivethe coagulated water, treat with flocculant, and separate secondparticles from the water, a second filter stage operative to filterthird particles from the water; and, an outlet.

In another aspect of the presently described embodiments, the firstfilter stage is a screen filter.

In another aspect of the presently described embodiments, the spiralstage is incorporated in a single spiral device.

In another aspect of the presently described embodiments, the mixingstage is incorporated in a single spiral device.

In another aspect of the presently described embodiments, the mixingstage is incorporated in a flash mixer.

In another aspect of the presently described embodiments, the spiralstage is incorporated in a first spiral device to receive the coagulatedwater and treat with flocculant and a second spiral device to separatesecond particles from the water.

In another aspect of the presently described embodiments, the secondfilter stage is a filter device.

In another aspect of the presently described embodiments, the systemfurther comprises a feedback path to the source.

In another aspect of the presently described embodiments, the feedbackpath includes a spiral stage for dewatering.

In another aspect of the presently described embodiments, the firstparticles are approximately 1-3 mm in diameter.

In another aspect of the presently described embodiments, the secondparticles are approximately 5 μm or larger in diameter.

In another aspect of the presently described embodiments, the thirdparticles are 0.5 μm or larger in diameter.

In another aspect of the presently described embodiments, the methodcomprises receiving water from a source, filtering the water to removefirst particles, flash mixing the filtered water with chlorine andcoagulant, slow mixing output of the first spiral stage with flocculantin a spiral stage, separating second particles in the spiral stage, and,filtering the output of the spiral stage to remove third particles.

In another aspect of the presently described embodiments, the filteringof the water to remove first particles comprises passing the waterthrough a screen.

In another aspect of the presently described embodiments, the slowmixing and separating are accomplished in a single separation device.

In another aspect of the presently described embodiments, the filteringof the output of the spiral stage comprises passing the output through afilter having multiple media or membrane filters.

In another aspect of the presently described embodiments, the methodfurther comprises dewatering in a feedback path.

In another aspect of the presently described embodiments, the firstparticles are approximately 1-3 mm in diameter.

In another aspect of the presently described embodiments, the secondparticles are approximately 5 μm or larger in diameter.

In another aspect of the presently described embodiments, the thirdparticles are 0.5 μm or larger in diameter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a conventional water treatment.

FIG. 2 is a typical timing diagram for stages of coagulation,flocculation, and sedimentation in a conventional water treatmentsystem.

FIGS. 3(a) and 3(b) illustrate systems according to the presentlydescribed embodiments.

FIGS. 4(a)-(c) illustrate an example of a spiral device designed for 1um particle cut-off and 100 L/min throughput.

FIG. 5 illustrates another embodiment;

FIGS. 6(a) and 6(b) illustrate still another embodiment;

FIGS. 7(a) and 7(b) show a Coulter counter quantification of particleextraction.

FIG. 8 is a chart showing a relation for particle size to NTU reading.

FIG. 9 is a chart showing typical cost of chemicals for coagulation andflocculation.

FIGS. 10(a) and 10(b) show coagulation and sedimentation times andsavings calculation.

FIG. 11 illustrates an experimental setup for jar test experiments.

FIG. 12 shows turbidity as function of time for a jar tests withstandard (sample B) and step-wise (sample A) coagulant addition.

FIG. 13 is a comparison of the measured turbidity data for two differentjar tests to a diffusion driven aggregation model.

FIGS. 14(a) and 14(b) show NTU data for a typical jar test experiment.The blue data shows the standard jar test results, the pink curve themodified jar test results. The inset shows the turbidity measurementsduring the first 30 minutes.

FIG. 15 shows fits of test data to Eqn. (7). Black: standard jar test;red: modified jar test; the solid line is the fit to the data points.

DETAILED DESCRIPTION

The presently described embodiments represent a transformationalapproach to water treatment that incorporates membrane-free filtrationwith dynamic processing of the fluid to significantly reduce treatmenttimes, chemical cost, land use, and operational overhead. The approachprovides hybrid capabilities of filtration together with chemicaltreatment as the water is transported through various spiral stages.

Features of the system include, but are not limited to, the following:

1) Use of a spiral particle extraction capability as a front-end tolighten the TSS (total suspended solids) loading on the system. Theflash mixing at the front-end of the process also enhances chemicalkinetics and results in a more complete reaction;

2) Use of a dynamic transport capability in narrow flow channels wherethe high rate of shear from rapid parabolic flow and coagulants resultsin seed particles of uniform size which are ideal for acceleratedagglomeration kinetics;

3) Allowance for removal of pin floccs (particle size at transitionpoint between the end of coagulation and start of flocculation) as smallas 5 μm by the spiral device rather than rely on the conventionalpractice of allowing them to agglomerate to hundreds of microns in sizebefore settling out in the sedimentation basin. This process alsoresults in accelerated agglomeration;

4) Allow for the entire or near elimination of the flocculation andsedimentation steps together with all the attendant chemicals. This willalso allow for reduced land use and maintenance labor; and,

5) Allow for gradual dosage of chemicals.

In this regard, FIGS. 3(a) and (b) show schematics of example watertreatment plants according to the presently described embodiments. Theseembodiments illustrate replacing selected components of the conventionalsystem with components shown within the inscribed ellipse of FIG. 3(a).Elimination of, for example, the flocculation step results in a reducedfootprint and a reduced use of chemicals.

As shown in FIG. 3(a), a system 100 is used to process water from awater source 102. The system includes a screen filter 104 operative toremove relatively large particles from the supply. These particles aretypically in the range of 1 mm to 3 mm. Other larger particles andobjects (e.g., fish, trash, etc.) are also filtered out through thisscreen. An optional pH adjustment may be made to the fluid as itproceeds through the system.

The system 100 further includes a first stage 106, a second spiral stage108 and a third spiral stage 110. It is to be appreciated that thespiral stages may be incorporated within a single spiral separatordevice. As an alternative, any one of the spiral stages may beimplemented in its own unique spiral separator device. In any case, thefirst stage 106 is a flash mixing stage. It should be understood thatthis stage may take the form of a flash mixer, a turbulent mixer oranother spiral mixing stage. If a spiral mixing stage is used here, asufficient amount of turbulence is introduced into the spiral stage toachieve sufficient mixing. The second spiral stage 108 is a spiral slowmixing stage. And, the third spiral stage is a spiral separating stage.In the third stage, particles of 5 μm or larger are typically separatedfrom the fluid.

A filter 112 is also provided to the system. The filter 112 may take avariety of forms. However, in one form, it comprises multiple filteringmedia or membrane filters to, for example, conform to EPA mandates forphysical barriers. The particles that are filtered by the filter device112 are typically in the 0.5 μm or larger range. Also shown in thesystem 100 is an optional spiral stage 114 that provides for dewatering.In this stage, the spiral dewatering device receives backwash fluid fromthe filter 112 and separates sludge from water which is provided back tothe water source.

In operation, the system 100 receives water from the source 102 whichmay include ground, surface, brackish, sea or waste water. This water isfiltered through the screen filter 104 to remove a first group ofparticles in the noted range. The water supply is then flash mixed instage 106 along with the potassium permanganate, coagulant, andchlorine. Next, flocculant is slow mixed into the supply in spiral slowmixing stage 108. In the third spiral stage 110, another group ofparticles is separated out from the supply. As noted, these particlesare typically in the 5 μm or larger range. Then, the filter 112 filtersout a third group of particles that are generally smaller and are in therange of 0.5 μm or larger. The output is then transmitted on for any ofa variety of uses.

It should also be understood that the filter 112 may be subjected to abackwashing process which will provide fluid to an optional spiraldewatering stage 114 to, again, separate sludge from water that isprovided back to the water source.

With reference now to FIG. 3(b), another embodiment is illustrated thatuses a flash mixer and a single spiral device to achieve desiredseparation. As shown, a system 101 includes screen filter 104 operativeto filter out relatively large particles from the supply (e.g.,particles/objects in the 1 mm to 3 mm range or larger). Also shown is aflash mixer 105 operative to flash mix coagulant and other suitablechemicals into the supply. Turbulent mixing may be achieved in the flashmixer 105 or in a separate device. A spiral device 109 is shown. Thespiral device 109 includes an inlet 107 and outlets 111 and 113. Thespiral device 109 effectively replaces the flocculation andsedimentation stage of conventional systems and is designed to achievesubstantially similar objectives through the use of spiral separation.Flocculant may be added at this stage as well.

The outlet 111 connects to a waste stream 115 which, as shown, includesparticles greater than 1-5 micrometers in size. Also shown is anoptional recirculation path 117 that may have disposed therein a reducedcoagulation tank 119. The recirculation path connects with the inlet 107of the device 109. The outlet 113 connects to a filter 112, whichoperates and is configured as described above in connection with FIG.3(a).

An example of spiral wound prototype of a spiral device is shown in FIG.4(a). The device is designed for 100 L/min throughput. As shown, FIG.4(a) illustrates a spiral device 200 that includes an inlet 202 and abody portion 204 that comprises at least one spiral channel thatconnects to an outlet 206. The outlet 206 comprises a split channelegress—a single channel egress 205 for effluent and a single channelegress 207 for concentrate. As shown in FIG. 4(b), the body 204 of thespiral device may be comprised of a single spirally wound channel 210.As an alternative, FIG. 4(c) shows an embodiment wherein the body 204 isdivided into eight parallel channels 210, 212, 214, 216, 218, 220, 222,and 224. It is to be understood that other numbers of parallel channelsare possible depending on desired throughput, manufacturing option, andfabrication cost.

The spiral device 200 may be structured so that a single spiral stage,as noted above, or multiple contemplated spirals stages are incorporatedtherein. Of course, the objectives of flash mixing, slow mixing andseparating are taken into account in the design of each of the stages.For example, the channel width and flow velocity of each of the stagesis taken into consideration in the spiral device implementation. In thisregard, it should also be understood that the spiral device shown ismerely an example. Any similar spiral device may be implemented toachieve the objectives of the presently described embodiments. Forexample, spiral devices described in U.S. application Ser. No.11/606,460, filed Nov. 30, 2006, entitled “Particle Separation andConcentration System,” or U.S. patent application Ser. No. 11/936,729,filed on Nov. 7, 2007, entitled “Fluidic Device and Method forSeparation of Neutrally Buoyant Particles,” and naming Lean et al. asinventors which are incorporated in their entirety herein by thisreference, may be used. It should be appreciated that any suitablematerial may be used to implement the spiral devices of the contemplatedsystem.

Further, the dimensions of the spiral channel may vary depending on theimplementation. In one form, however, the diameter of the spiral deviceis 12 inches and the height may vary from 1 inch to 16 inches. Thedimensions may have an impact on pressure and output power of thesystem. Likewise, dimensions of the actual channels may impact pressureand power output. Generally, more pressure (which can be a result of anarrow channel) will result in more power.

Also, the device may be cascaded and/or placed in parallel to achievegreater control of the output and/or greater throughput through thesystem. As a mere simple example used for explanatory purposes, withreference now to FIG. 5, a further embodiment to the presently describedembodiments is shown. In this embodiment, a purification system 500includes a two-stage spiral separation system to isolate particles ofdifferent sizes. In the example system shown, the particles are isolatedin a 1 to 10 micrometer range. As shown, the system includes an inputwater source 502 connecting to a spiral separator 504 having an inlet506, as well as a first outlet 508 and a second outlet 510. The secondoutlet 510 is connected to a second spiral separator 520 by way of aninlet 522. The spiral separator 520 includes a first outlet 524 and asecond outlet 526 as shown.

In operation, the system 500 with the cascaded spiral stages facilitatesa first separation of particles between those of greater than 10micrometers being output from the first spiral separator in a wastestream and particles less than 10 micrometers being input to the secondspiral separator 520 for further processing. The second spiral separatorthen separates particles greater than 1 micrometer and outputs fluidwithin which those particles reside by way of outlet 524. The remainingfluid or effluent is output through outlet 526. In this manner, thesystem 500 is able to isolate particles between 1 and 10 micrometers forvarious sampling processing. This concept can be extended by continuedcascading of spiral structures with smaller size cut-offs to achievefractionation of particles with decreasing size ranges.

With reference to FIGS. 6(a) and 6(b), an example parallel system isshown. The embodiment of FIG. 6(a) shows a spiral device 700 that is aspiral wound device. Other types of spiral devices may also be used—thisis simply an example. In this regard, other examples of spiral deviceimplementations are shown in and commonly assigned, co-pending U.S.patent application Ser. No. 11/936,729, filed on Nov. 7, 2007, entitled“Fluidic Device and Method for Separation of Neutrally BuoyantParticles,” and naming Lean et al. as inventors.

This device 700 includes a spirally wound body 704 having inlet 706, afirst outlet 708 and a second outlet 710. The device 700, as shown inFIG. 6(b), may be disposed in a system wherein a plurality of devices700 are connected in parallel to a water inlet main 720 from a fluidmanifold. Similarly, the first outlet lines for the devices areconnected to a first outlet main 722. The second outlet lines of thedevices 700 are connected to a second outlet main 724.

In FIG. 7(a), the quantified results using a Coulter Counter are shownwhere 300 times difference in concentration are seen at the particulateoutlet at 99.1% extraction efficiency. The device can be furtheroptimized to improve performance. In FIG. 7(b), the single channel 210having the egress channel 205 and concentrate channel 207 is shown. Theparticles subject to separation are shown at 211.

FIG. 8 contains data to estimate the cost advantage in adoption of thepresently described embodiments. Daily potable water usage in the US in2000 is 43,300 MGD, representing 10.6% of total water consumption. Totalchemical cost for coagulation and flocculation is $2B to $4B dependingon source waters. The total annual US market for potable water is $41B.Turbidity in nephelometric units (NTU) is a uniform metric used in thewater industry to determine the type and level of water treatment. Thisis a measure of optical transmission and scattering, and includeseffects of particle size, density, and color. By using the spiral deviceto reduce particles in the effluent stream to sub-micron size, theturbidity is reduced to less than 0.78 NTU (FIG. 8). Using the data inFIG. 9, the reduction in turbidity of 23 NTUs would result in chemicalcosts of $2.1B per year (43,300×23×5.79=$5.766 M/day@2.104B/year). FIGS.10(a) and 10(b) show the combined coagulation and sedimentation timesbased on estimated rates of agglomeration assuming that a 30 nm particlegrows into a 1 μm particle in 20 minutes. For a combined coagulation andsedimentation time of less than 4 hours, a suitable particle size is 70μm in 44 minutes. Assuming that flocculant costs are 50% of the totalchemical cost, the savings in eliminating the flocculant step is $698Mfor the year. The numbers used here are representative of the chemicalcost advantage of the spiral device. Other cost advantages include landcost and associated construction cost.

Dynamic processing of the water during transport through the variousspiral stages refers to the use of coagulants and high shear rates toenhance agglomeration kinetics. Proof of concept is demonstrated inwater treatment experiments using conventional jar tests with andwithout a spiral device. Jar tests are a standard lab-scale procedurefor optimizing the aggregation/flocculation/sedimentation dosage andperformance in the water treatment process. The type and amount ofcoagulant needed depends on the turbidity and native pH of the samplewater. Our sample water had a turbidity level of between 25 to 30 NTUand a native pH value of about 9. The standard jar test is typicallyperformed in three phases: In the first phase the liquid is stirred at ahigh rate (e.g. 275 to 280 rpm) during which the coagulant is addedrapidly and the pH level of the sample is adjusted to a value of 9 using1 N NaOH solution. In a second phase stirring is reduced to a moderatelevel (e.g. 25 to 30 rpm) that promotes some mixing, but allows thegrowth of larger floccs. In the third phase no external stirring takesplace while the particles grow even larger and sediment out of solution.

In a first modification of the standard jar test (subsequently referredto as “step wise coagulant addition”) we added the coagulant graduallyin small doses, and adjusted the pH level to a value of 9 after each ofthese additions.

In a second modification (subsequently referred to as “modified jartest”), we pumped the fluid at a fixed flow rate through a spiralchannel device during phase 1, and optionally during phase 2. Theaverage shear rate inside the channel is approximately 300/s,corresponding to a conventional square jar. In comparison, the averageshear rates inside the cylindrical glass beaker are 100/s and 10/s forthe rapid and slow mixing phases, respectively.

FIG. 11 shows the experimental setup 1000 for the jar tests. Theaggregation and flocculation is performed in a 1000 ml glass beaker1001. Mixing is achieved with a marine turbine rotor and/or stirrer 1012that can be operated at different speeds. For the modified jar test, anadditional peristaltic pump 1003 is used to push the liquid through aspiral channel 1004. The fluid inlet 1005 and outlet 1006 are submergedbut well above the bottom to prevent sediment pickup. They are alsolocated diametrically across from each other. In all the experimentsturbidity values are recorded at frequent time intervals to monitor theprogress of the flocculation. Other test devices in the set-up 1000 arealso illustrated but not specifically discussed for ease of explanation.

There are different modes of aggregation: For small particles and/orslow stirring diffusion driven aggregation dominates. For largerparticles (approx 1 μm and above) and/or higher mixing rates aggregationis shear dominated. In this case the maximum particle size is limited,since the shear force on the particles will increase with the aggregatesize and eventually exceed the binding force between the individual(primary) particles. Most of the particle aggregation and flocculationhappens while the sample liquid is not agitated or only moderatelystirred. In this case, diffusion driven aggregation is the dominantgrowth mode for particles below a few μm in size. The total particlenumber decreases over time as

$\begin{matrix}{{{N(t)} = \frac{N_{0}}{1 + {t/\tau}}},} & (1)\end{matrix}$where N₀ is the particle concentration at the start of the experiment, tis time, and τ is the characteristic time scale of the process. For thediffusion driven (or perikinetic) aggregation τ depends on the fluidviscosity, temperature, the initial concentration of particles, and thetype of aggregates that grow (loose and light vs. compact and dense).

Turbidity is a measure that includes both light absorption as well aslight scattering off particles. Though it is not an exact measurement ofthe particle concentration or size distribution inside the sampleliquid, we may still expect a similar time dependence of the NTU value,if particle scattering dominates the measured value. To compare measuredturbidity vs. time curves with model predictions, we fit theexperimental data to the function

$\begin{matrix}{{{f(t)} = {\frac{b_{0}}{t + b_{1}} + b_{2}}},} & (2)\end{matrix}$which was derived from Eqn. (1) by adding a time offset and a constantbackground:

$\begin{matrix}{{{N\; T\;{U(t)}} = {\frac{f\left( N_{0} \right)}{1 + {8\pi\;{{DrN}_{0}\left( {t - t_{0}} \right)}}} + {N\; T\; U_{base}}}},} & (3)\end{matrix}$withb ₀ =τf(N ₀); b ₁ =τ−t ₀ ; b ₂=NTU_(base).  (4)

Comparison of Standard Jar Test Vs. Step-Wise Coagulant Addition

To start the aggregation process coagulant is added and the pH isadjusted to an alkaline level of about 9. The rate and order of additionof these two substances to the sample liquid matter, as they define theionic strength of the solution and the surface charge of the colloidalparticles. Rapid mixing at this stage is essential, as the coagulantdestabilizes the sample solution at the injection point and leads to theformation of very large, but loosely connected, floccs that increase thelocal viscosity substantially. Sufficient shear will break up this floccnetwork and promote good mixing of all the coagulant within the samplevolume. In the standard jar test, all the coagulant is added first at arapid rate, and then the pH is adjusted with 1 N NaOH solution. Here wecompare this standard process with a step-wise procedure, where thecoagulant is added in small amounts, followed by an immediate adjustmentof the pH level with NaOH solution.

FIG. 12 shows turbidity measurements as a function of time for both ofthese approaches on a dirt water sample using alum as the coagulant. Thecoagulant (80 mg/L) and NaOH is added at the beginning of a 5 minuterapid mixing phase, which is followed by a 25 minute slow mixing phasebefore the aggregates are allowed to settle. In the step-wise procedure,the coagulant was added in 8 steps of 10 mg, each. The total amount ofNaOH solution needed to adjust the final pH to 9 varied between 1.1 mlfor the standard to 1.2 ml for the step-wise coagulant addition process,suggesting a slight difference in either the ionic composition of thesolution and/or the surface charge on the colloidal particles. From FIG.10 we see that the step-wise addition of the coagulant followed by animmediate pH adjustment leads to a faster and more complete reduction ofthe turbidity. FIG. 13 shows a comparison of the experimental data withthe model predictions. Eqn. (8) fits the data quite well, suggestingthat the perikinetic model is a good description of the aggregationprocess in both of these jar test experiments. Assuming that we startwith the same initial concentration of colloidal particles, and that wekeep the temperature in both experiments the same, the fasteraggregation rate for the step-wise coagulant process suggests that thecolloidal particles form denser aggregates that diffuse faster throughthe solution. In other words, maintaining the pH close to the native pHof our sample water during coagulant addition helps in the formation ofcompact seed floccs that consequently lead to faster aggregation.

Comparison of Standard Jar Test Vs. Modified Jar Test

FIGS. 14(a) and (b) compare turbidity measurements for a standard and ajar test experiment which uses an additional spiral device. In thiscase, the sample was stirred initially at a high rate. After 3 minutesthe stirrer was turned off. In the modified setup, the liquid was pumpedat a flow rate of 333 ml/min through a spiral channel with a 3 by 3 mm²cross section for the 3 minutes of rapid stirring and for another 27minutes afterwards. At this flow rate the average shear rate inside thechannel is about an order of magnitude larger than the average shearrate inside the cylindrical beaker (during phase 1). For the standardjar test, NTU readings drop immediately after the rapid stirring wasstopped (square annotated curve). In the modified jar test, the NTUreadings stayed high throughout the 30 minutes while the sample fluidwas pumped through the channel (see FIG. 14(b)), but dropped even morerapidly thereafter (circle annotated curve). The substantially highershear rate within the fluidic channel will cause a more severe break-upof the initial floccs that have formed immediately after the coagulantaddition, and only small and very compact floccs (primary particles)will have survived. On the other hand, during the minutes while thesample fluid was circulated through the channel, all the coagulant waswell mixed within the sample and rapid aggregation started after thepump was turned off. In the standard jar test, loose floccs that formdoes not break up even during rapid mix. Because of their large size,they will diffuse more slowly than more compact aggregates andcompletion of the growth process will be slower.

FIG. 15 shows fits of the experimental data to the perikineticaggregation model of Eqn. (3). Again, the fits are excellent; suggestingthat the turbidity decrease seems to be closely related to the reductionof total particle number in solution. The more rapid drop-off in theturbidity readings at long times is most likely caused by sedimentation,which is not included in the fit model, but is expected to have a largereffect on compact particles then on loose floccs.

In summary, the aggregation dynamics depends crucially on the rate andmode of coagulant addition and pH adjustment. Initial inhomogeneities inthe coagulant concentration appear to create large loose floccs that donot break up even under the applied stirring rate. These loose floccshave a low diffusion rate due to their large size which leads to aslower growth rate. Step-wise coagulant addition with immediateadjustment of the pH of the sample liquid prevents the uncontrolledgrowth of large, loose floccs and promotes the formation of more compactaggregates that grow faster due to their faster diffusion rates. Movingthe sample fluid through a channel at sufficient flow rate (causingsufficiently large shear rate) will prevent aggregate growth and willlead to break-up of the loose floccs that form during coagulantaddition. Once the sample liquid is no longer moving through the microchannel, aggregates grow rapidly, suggesting again the formation ofcompact particles.

The advantages of the presently described embodiments include:

1) Particulate extraction based on design cut-off down to 1 um

2) Dynamic processing—transport and enhancement of agglomerationkinetics

3) Replacement of intermediate filtration steps

4) Front-end to MWT to lighten the TSS loading

5) Cascaded operation

6) Parallelizable operation

7) Scalable, high-throughput, continuous flow

8) Shorter processing time, smaller footprint, reduce TCO (total cost ofownership)

9) Elimination of flocculation and sedimentation steps—savings onchemicals, land, and operating incidentals including labor, power, etc.

10) May be used for other applications in water including but notlimited to IC fab reclaim, cooling tower water, MBR (membrane bioreactor), pre-treatment for RO (reverse osmosis), and waste waterreclaim.

It will be appreciated that various of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also thatvarious presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art which are also intended to beencompassed by the following claims.

The invention claimed is:
 1. A system for dynamic processing for waterpurification, the system comprising: an inlet to receive water from asource; a filter stage operative to filter first particles; a mixingstage operative to receive and coagulate the filtered water; a spiralstage operative to receive the water and separate second particles fromthe water, wherein the spiral stage comprises a channel in whichseparation occurs, having a central inlet, structured to providecontinuous flow to a peripheral outlet thereof having a split channelegress with a first single channel egress for effluent and a secondsingle channel egress for concentrate; and a second filter stageoperative to filter third particles from the water.
 2. The system as setforth in claim 1 wherein the first filter stage is a screen filter. 3.The system as set forth in claim 1 wherein the spiral stage isincorporated in a single spiral device.
 4. The system as set forth inclaim 1 wherein the mixing stage is incorporated in a single spiraldevice.
 5. The system as set forth in claim 1 wherein the mixing stageis incorporated in a flash mixer.
 6. The system as set forth in claim 1wherein the spiral stage is incorporated in a first spiral device toreceive the coagulated water and treat with flocculant and a secondspiral device to separate second particles from the water.
 7. The systemas set forth in claim 1 wherein the second filter stage is a filterdevice.
 8. The system as set forth in claim 1 further comprising afeedback path to the source or to the inlet of the channel.
 9. Thesystem as set forth in claim 8 wherein the feedback path includes aspiral stage for dewatering that receives backwash from the secondfilter stage.
 10. The system as set forth in claim 1 wherein the firstparticles are approximately 1-3 mm in diameter.
 11. The system as setforth in claim 1 wherein the second particles are approximately 5 μm orlarger in diameter.
 12. The system as set forth in claim 1 wherein thethird particles are 0.5 μm or larger in diameter.
 13. A system fordynamic processing for water purification, the system comprising: aninlet to receive water from a source; a filter stage operative to filterfirst particles; a spiral mixing stage operative to receive andcoagulate the filtered water, the spiral mixing stage having a centralinlet and a peripheral outlet; a separating stage operative to receivethe coagulated water and treat with flocculant and separate secondparticles from the water, wherein the separating stage comprises achannel in which separation occurs, having an inlet, structured toprovide continuous flow to an outlet thereof having a split channelegress with a first single channel egress for effluent and a secondsingle channel egress for concentrate, wherein the separating stageeliminates sedimentation to separate the second particles; a secondfilter stage operative to filter third particles from the water.
 14. Thesystem as set forth in claim 13 wherein the first filter stage is ascreen filter.
 15. The system as set forth in claim 13 wherein thesecond filter stage is a filter device.
 16. The system as set forth inclaim 13 further comprising a feedback path to the source.
 17. Thesystem as set forth in claim 13 wherein the first particles areapproximately 1-3 mm in diameter.
 18. The system as set forth in claim13 wherein the second particles are approximately 5 μm or larger indiameter.
 19. The system as set forth in claim 13 wherein the thirdparticles are 0.5 μm or larger in diameter.
 20. The system as set forthin claim 1 wherein the channel is membrane-free.
 21. The system as setforth in claim 13 wherein the channel is membrane-free.
 22. A system fordynamic processing for water purification, the system comprising: aninlet to receive water from a source; a filter stage operative to filterfirst particles; a spiral mixing stage operative to receive, coagulateand mix flocculant into the filtered water, the spiral mixing stagehaving a central inlet and a peripheral outlet; a spiral separatingstage operative to receive the water from the mixing stages and separatesecond particles from the water, wherein the spiral stage comprises achannel in which separation occurs, having a central inlet, structuredto provide continuous flow to a peripheral outlet thereof having a splitchannel egress with a first single channel egress for effluent and asecond single channel egress for concentrate; and, a second filter stageoperative to filter third particles from the water.
 23. The System asset forth in claim 22 further comprising a water feedback path.
 24. Asystem for dynamic processing for water purification, the systemcomprising: an inlet to receive water from a source; a filter stageoperative to filter first particles; a spiral stage operative to receivethe water, mix the water and separate second particles from the water,wherein the spiral stage comprises a channel in which mixing andseparation occurs, having a central inlet, structured to providecontinuous flow to a peripheral outlet thereof having a split channelegress with a first single channel egress for effluent and a secondsingle channel egress for concentrate; and a second filter stageoperative to filter third particles from the water.